Can I set a data transfer limit to prevent overages?

There's no way to set a hard limit in the Linode Manager but you can set up automatic email alerts if you'd like. That way you'll be alerted if there's any unusual resource usage.

You could also set up a quota in iptables if you'd like, which is a special rule that stops matching after it reaches a set quota. We have a guide on using iptables in general here.